1. Field of the Invention
The present invention relates to a static pressure bearing and a transport device utilizing the same, and more particularly to such a static pressure bearing and transport device adapted for use in a semiconductor device producing apparatus.
2. Description of the Prior Art
In a static pressure fluid bearing, in case of regulating the distance between the fluid emitting pads and the supporting surface by means of a change in the fluid supply pressure, it is desirable that the ratio or sensitivity of change in said distance to the change of fluid supply pressure be regulatable. Generally a change in the fluid supply pressure to the pads causes a change in the distance between the pads and a supporting surface, but it was found that a change in distance resulting from a supply pressure change by 500 g/cm.sup.2 from 5 kg/cm.sup.2 is different from that caused by a supply pressure change of 500 g/cm.sup.2 from 4 kg/cm.sup.2. In this manner the sensitivity varies according to the reference pressure. Also in such a bearing, the sensitivity is inevitably unstable if the fluid pressure is controlled only in the region of the gap. Thus, although the sensitivity control itself is important, it is necessary for this purpose to strictly control the flatness of guide members, dimensional precision of sliding parts and pads, and rigidity and floating force of the pads. However such control of the error or fluctuation in the precision of component parts or in the characteristic of pads practically has certain limitations, and inevitably reduces the productivity.
On the other hand, the production technology for integrated circuits and large-scale integrated circuits in the semiconductor industry is showing remarkable progress. In such production, a process of printing a circuit pattern of a photomask onto a photosensitive layer of a wafer required a particularly advanced optical technology since the line width constituting said circuit pattern is of sub-micron dimension. For this purpose there is already known, for example, an exposure apparatus in which large convex and concave mirrors are positioned in mutually opposed manner to form an image of real size by a light beam repeatedly reflected between said mirrors and to intercept said beam, except at an annular field, of satisfactory image quality thereby scanning the mask and wafer respectively placed on the object plane and image plane.
In such exposure apparatus the highly precise transportation of mask and wafer is an essential factor for satisfactory image formation, and for this purpose the Japanese Patent Laid-open Sho54-53867 proposes a transport device. However the guide rails guiding the members to be transported can hardly achieve highly precise linearity because of the required considerable length, and are unable to maintain the linearity for prolonged periods. Consequently the mask and wafer sliding along such guide rails may locally be inclined two-dimensionally to generate aberration in the image, thus hindering improvement in the performance of the semiconductor device.
The Japanese Patent Laid-open Sho58-25637 of the present applicant discloses compensation for non-linearity of the guide rails by providing the member transported along the guide rails with floating elements, such as plural air pads of inverted saucer shape for emitting air of a determined pressure and varying the distance to the guide rails by regulating the floating force of said pads thereby controlling the position of said member.
However simultaneous control of the floating force of plural floating elements tends to result in yawing and rolling in the transported member if the precision of the guide rails or the combined precision of the guide rails and floating members is insufficient or if the performance of plural floating elements is not uniform.